This invention relates to a seal assembly for connecting two pieces of a pipeline or conduit, one of which has a plain end and the other a socket end. More specifically, the invention concerns a seal for connecting a large-diameter pipe (D&gt;800 mm) having spigot and socket ends, to other pieces such as an elbow with two sockets, a T-pipe with two sockets, or even a connecting sleeve with two sockets.
French Pat. No. 2,094,278 discloses a seal for joining two pieces of a pipeline or conduit, one having a plain end and the other a socket end, formed by inserting a gasket that is compressed radially between the inner surface of the socket and the outer surface of the plain end.
In this type of seal, the gasket is placed between the spigot end and the socket only after the spigot end has been inserted within the socket. This makes it possible to set the spigot into the socket without a great deal of effort.
After the gasket has been set into place, the insertion of means for closing off the socket, which may consist of a ring nut or a bayonet ring or even a mating flange fastened to the outer surface of the socket, prevents the gasket from being pushed out of the socket when the pipeline or conduit is pressurized.
In this type of seal the gasket, in its free state, has an inner diameter that is close to the outer diameter of the spigot end onto which it is to be placed. Once slipped over the spigot end, but before being compressed by the socket, it exerts no force. It is thus necessary in setting the gasket between the spigot and socket to employ a level of force that may be quite high, if not totally prohibitive, and that in any event will require the use of complicated and heavy equipment.
Furthermore, once the gasket is set, either the inner surface of the socket must be threaded, or a mating flange with numerous bolts must be installed. In either case, the field installation of such a seal becomes very difficult if not impossible, given the size of the pieces being handled (in the case of pipelines or conduits with a diameter greater than 800 mm) and the gripping force involved.